Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$108.61	10.242%	$119.7338	$119.73	$119.75	$119.70
Purchase #2	$35.80	9.641%	$39.2515	$39.25	$39.25	$39.30
Purchase #3	$69.32	13.209%	$78.4765	$78.48	$78.50	$78.50
Purchase #4	$27.89	10.504%	$30.8196	$30.82	$30.80	$30.80
Purchase #5	$38.31	5.662%	$40.4791	$40.48	$40.50	$40.50
Purchase #6	$154.26	9.813%	$169.3975	$169.40	$169.40	$169.40
Purchase #7	$167.27	12.741%	$188.5819	$188.58	$188.60	$188.60
7 purchase totals =	$601.46		$666.7399	$666.74	$666.80	$666.80